Isolated segments of small intestine from Amphiuma actively absorb Cl- by an electrogenic process that requires the presence of Na ion and HCO3- (and CO2) in the media. The intestinal absorptive cells lining the villus accumulate Cl- across the mucosal membrane when Na ion is present in the media. Cl- selective microelectrodes will be used further to determine how the stilbene SITS, which inhibits net Cl-absorption, affects the accumulation of Cl- by the villus absorptive cell and the mucosal membrane potential. Agents which are likely to stimulate metabolism, such as glutamine, will be examined for their effect on net Cl- absorption and Cl- accumulation. This information will allow an assessment of the role of intracellular HCO3- in the overall Cl- transport process. Total cell chloride will also be determined using conductimetric titration with estimation of inulin extracellular space under normal conditions and following incubation in various media (Na ion-free, HCO3-free and in the presence of acetazolamide, SITS and other agents known to alter Cl transport). Combined with previously determined values of intracellular chloride activity some conclusions about the mobility of the bound pool of cytoplasmic chloride, already known to exist, will be drawn.